1. Field of the Invention
The present invention relates to a tripod type constant velocity universal joint, for example, for use in a drivetrain of an automobile drive system and for transmission of a rotating force at a constant angular velocity between two rotary shafts on a nonlinear line of the automobile drive system.
2. Description of the Background Art
Demand of weight reduction and size reduction of tripod type constant velocity universal joints is increasing to improve automobile mileage. Responding to the demand, a tripod type constant velocity universal joint of, for example, Japanese unexamined patent publication 2004-257418 is proposed. The tripod type constant velocity universal joint set forth in this Japanese unexamined patent publication 2004-257418 is of a double roller type where each outer roller rolls in parallel to a track groove. The journal root portion has a non-circular cross-section in which a diameter in the joint circumferential direction is larger than that in the joint axial direction. This feature brings about lightweight, compactness and reduced cost of the joints while keeping the strength at the root portion of the trunnion journal that tends to be a weakest portion of the trunnion.
However, in the event that an ultimate design is applied to the tripod type constant velocity universal joint of Japanese unexamined patent publication 2004-257418 in order to promote a lightweight compact conversion, it has been found out that it is insufficient to solely make the cross section of the journal root portion noncircular to maintain the strength at the root portion of the trunnion journal. That is, considering the strength of the whole tripod type constant velocity universal joint, it has been found it is difficult to promote a lightweight compact conversion of the whole tripod type constant velocity universal joint unless dimensions of each component, particularly, the shape and the dimensions of the roller cassette and trunnion journal root portion are optimally designed.